Can I re-use an existing order to populate my shopping cart?

Yes, and its very easy. Just follow these steps:

1. In the top-left corner of the website, click on the link to Sign In.
   (If you're already signed in, just click on the My Account link, located in the same place)
   
   
2. Once you've logged in, and at the My Account screen - click on completed orders - which you'lll find on the left-hand side.
3. You'll now be shown a list of your recent orders. Simply find the one you want to use as your starting point, then press the shopping cart icon to the right of that order (highlighted below in red).
   
   
4. And that's it. The items will be added to your cart, so you can either start the checkout process, or add any additional items you need before checking out.